In John Rawls' basement lab at the University of North Carolina at Chapel Hill, thousands of spotted and striped zebrafish swim in their shoe box-sized tanks. Some of the eggs the fish lay Rawls will make sterile after fertilization - each time creating a new chance to examine the relationship between gut microbes and their host environments.
Rawls first started working with zebrafish in 1996 during his graduate work
at Washington University in St. Louis, where he studied the cellular mechanisms
involved in pigment patterning.
In 2000 Rawls met with Gordon. Both agreed that the zebrafish's transparent body would be a novel way to observe the digestive tract and its microbes, says Rawls. He joined the Gordon lab.
Rawls' first task was to define the minimal steps required to establish zebrafish as a model system. The zebrafish had to be germ-free in order for Rawls to study the effect of particular microbes on gene expression. Rawls would have to sterilize the eggs using the right concentration of germicidal treatment - a significant challenge, as he remembers.
Using a set of old papers describing how to make other fish species germ-free
by stripping the embryo of its protective chorion layer, Rawls succeeded in making
zebrafish germ-free in about seven months. Next, Rawls used microarray data to show
that, in germ-free zebrafish, microbiota induce gut gene
"John is certainly a star," writes his graduate advisor Stephen Johnson from Washington University in St. Louis in an E-mail. "Work from many labs on mice and humans shows that our gut microbes may have profound effects on our development and physiology. John watches these microbes perform in the [zebrafish] gut, something we can't even imagine for mammalian studies."
Another researcher, Karen Guillemin from the Institute of Molecular Biology at the University of Oregon, independently developed a similar protocol for zebrafish and has been using the system to look at the host effects on gastric pathogens. "We've benefited enormously from the knowledge base that [Rawls has] generated," she says.
To examine how host environments influence the composition of gut microbial
communities, Rawls took conventional gut microbiota from zebrafish and colonized the
bacteria in germ-free mice, and the reverse. He then surveyed the two microbial
communities, finding that the zebrafish and mice guts significantly shape the
composition of bacterial communities, especially the relative abundance of the
different types of bacteria.
As Rawls continues to look at gut-microbe interactions, he will try to raise zebrafish to later stages of development and successive generations, a challenge that will involve understanding the nutritional requirements for the germ-free zebrafish. "He's really making big strides in that area," Guillemin says.
Title: Assistant professor of cell and molecular physiology, University of
North Carolina at Chapel Hill
1. J.F. Rawls and S.L. Johnson, "Zebrafish kit mutation reveals primary and secondary regulation of melanocyte development during fin stripe regeneration," Development ,127: 3715-24, 2000. (Cited in 38 papers) 2. J.F. Rawls et al., "Gnotobiotic zebrafish reveal evolutionarily conserved responses to the gut microbiota," Proc Natl Acad Sci, 101:4596-601, 2004. (Cited in 60 papers) 3. J.F. Rawls et al., "Reciprocal gut microbiota transplants from zebrafish and mice to germ-free recipients reveal host habitat selection," Cell, 127:423-33, 2006. (Cited in 30 papers)